Is 70% Humidity Too High for Books?

Is 70% Humidity Too High for Books? 

A Library Science Perspective

Books are timeless vessels of knowledge. Whether preserved in libraries, archives, or personal collections, maintaining them in good condition is a major concern. Among the many environmental threats to books, humidity plays a critical role. But is 70% humidity too high for books? In the realm of library science, the answer is yes—and here's why.


Understanding Humidity and Its Effects on Books

Humidity refers to the amount of moisture in the air. It is typically measured as relative humidity (RH), expressed in percentage. A certain level of RH is necessary for human comfort, but when it comes to books, excessive humidity can cause significant damage.

Books are primarily made from organic materials—paper, leather, adhesives, and cloth—all of which are highly sensitive to environmental changes. When RH exceeds 60%, these materials begin to absorb moisture, which triggers a chain of destructive reactions.


Why Is 70% Humidity Dangerous for Books?

From a library preservation standpoint, 70% RH is considered excessive. Here's what can happen:

1. Mold and Mildew Growth

Mold spores thrive in environments with RH above 65%. At 70% humidity, mold can grow within 48 hours. Mold not only damages books irreversibly but also poses health risks to library users and staff.

2. Paper Degradation

Excess moisture accelerates the acid hydrolysis process in paper, causing yellowing, brittleness, and eventual disintegration.

3. Ink Bleeding and Adhesive Breakdown

High humidity can cause ink to run or smudge, especially in older manuscripts. It also breaks down adhesives, causing book bindings to weaken or fall apart.

4. Pest Infestation

Damp environments attract silverfish, booklice, and termites, all of which feed on paper and glue.

5. Physical Warping

Books may swell, warp, or curl, especially when humidity fluctuates. This makes them hard to shelve and damages their physical integrity.


Ideal Humidity Levels in Libraries

According to preservation guidelines from institutions like the Library of Congress and the International Federation of Library Associations (IFLA), the recommended RH for book storage is:

  • Ideal Range: 45% to 55%

  • Acceptable Range: 35% to 60%

  • Too High: Above 60% (risk of mold and degradation)

Therefore, 70% humidity is beyond acceptable limits for any library or archive setting.


Library Science Recommendations for Humidity Control

Professionals in library and information science (LIS) stress environmental control as a top priority in collection preservation. Here's how to manage high humidity:

1. Use Dehumidifiers

Invest in high-quality dehumidifiers for spaces where RH exceeds 60%. These are essential tools in tropical or coastal climates.

2. Install Hygrometers

Place digital hygrometers throughout the library to monitor RH in real time. Monitoring allows for prompt corrective action.

3. Air Conditioning

Modern HVAC systems not only cool the air but also regulate moisture. Ensure your system has humidity control features.

4. Ventilation

Proper airflow reduces damp spots and prevents mold buildup. Open windows periodically, if outdoor humidity is lower.

5. Avoid Basement Storage

Basements are naturally humid and poorly ventilated. If you must store books there, use industrial dehumidifiers and silica gel packs.

6. Use Archival-Quality Materials

Acid-free boxes, Mylar covers, and buffered folders help protect books from moisture absorption.


Special Considerations for Tropical Countries

In countries like Sri Lanka, India, and other tropical regions, humidity often stays above 70%. Libraries here face constant challenges. Some local solutions include:

  • Using charcoal or salt-based moisture absorbers in small spaces

  • Building with natural ventilation and high ceilings

  • Organizing community awareness programs on book care


Case Studies in Library Science

National Library of Sri Lanka

The National Library faced repeated issues with mold outbreaks in the 1990s due to high humidity. After installing centralized air conditioning and relocating rare books to climate-controlled rooms, mold incidents reduced by 85%.

British Library Preservation Centre

They maintain an RH of 50% ± 5% using advanced HVAC and automated monitoring systems. This setting is a model for all institutions aiming to preserve rare manuscripts and archives long-term.


Humidity and Digital Archives

Even as libraries shift toward digitization, original physical copies must be preserved. High humidity can destroy irreplaceable historical texts, maps, and manuscripts before digitization even begins. Therefore, climate control remains essential.


Conclusion: Keep Humidity Under 60%

Is 70% humidity too high for books? Absolutely. In the eyes of library science experts, it’s not just unfavorable—it’s hazardous. To ensure the long-term preservation of books, a stable environment with humidity between 45% and 55% is ideal.

Investing in environmental controls today saves books for generations tomorrow. Whether you're managing a large public library or a small personal collection, understanding and acting on humidity risks is a non-negotiable part of responsible book stewardship.

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